State law prohibits vanity plates that "a reasonable person would find offensive to good taste." But the New Hampshire Civil Liberties Union argued that the law is unconstitutionally vague and gives too much discretion to a person behind a Department of Motor Vehicles counter.

New Hampshire had argued that state workers were right to deny the plate, because the phrase disparages an entire class of people - police officers.

The justices said that state law does not define the phrase "offensive to good taste."

"The restriction grants DMV officials the power to deny a proposed vanity registration plate because it offends particular officials' subjective idea of what is 'good taste,'" the court wrote. The decision states the law is unconstitutionally vague and violates free speech rights.

The case was sent back to Strafford County Superior Court for further proceedings.

Attorney Anthony Galdieri, who argued the case on behalf of Montenegro and the New Hampshire Civil Liberties Union, said he was not surprised by the ruling. "This regulation was an impermissible way to regulate speech under the First Amendment," Galdieri said.

Montenegro did not immediately return a phone call seeking comment.

At spirited arguments in November, the high court panel grilled state officials.

"So if a person at DMV agrees with the sentiment, he gets the plate?" Chief Justice Linda Dalianis asked.

"What is good taste?" added Justice Carol Ann Conboy, who wrote Wednesday's ruling. "That seems to be the nub of the argument."

Answering a question about whether a plate reading "COPS R GR8" would be approved, Senior Assistant Attorney General Richard Head acknowledged that two different people could come to different conclusions. Head could not be reached for comment.

Lawyers for Montenegro told the court that the accusation "COPSLIE" is a viewpoint that should be protected as free speech, not regulated and suppressed by the government.

After court in November, Montenegro - who in 2012 legally changed his name to "human" - said he thought police officers who might pull him over and have to type "COPSLIE" into their computers would amount to "the perfect situational irony."

He also acknowledged that he had been arrested twice but would not say what the charges were.

License plates Mass. won't let you have

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Thousands of drivers across the state of Massachusetts have vanity license plates on their vehicle.

Most combinations don't draw the attention of the Registry of Motor Vehicles, but we recently scanned their rejection list to see what combinations have been denied.